The presence of volatile organic compounds (“VOCs”), semi volatile organic compounds (“SVOCs”) or pesticides in subsurface soils and groundwater is a well-documented and extensive problem in industrialized and industrializing countries. Many VOC's and SVOC's are compounds which are toxic or carcinogenic, and which are often capable of moving through the soil under the influence of gravity and serve as a source of water contamination by dissolution into water passing through the contaminated soil. Illustrative of such organic contaminants are compounds such as trichloroethylene (TCE), vinyl chloride, tetrachloroethylene (PCE), methylene chloride, 1,2-dichloroethane, 1,1,1-trichloroethane (TCA), carbon tetrachloride, chloroform, chlorobenzenes, benzene, toluene, xylene, ethyl benzene, ethylene dibromide, methyl tertiary butyl ether (MTBE), polyaromatic hydrocarbons, polychlorobiphenyls, phthalates, 1,4-dioxane, nitrosodimethyl amine, and methyl tertbutyl ether.
In many cases discharge of these compounds into the soil leads to contamination of aquifers resulting in potential public health impacts and degradation of groundwater resources for future use. Treatment and remediation of soils contaminated with VOC or SVOC compounds may be expensive, require considerable time, and in many cases be incomplete or unsuccessful. Treatment and remediation of volatile organic compounds that are either partially or completely immiscible with water (i.e., Non Aqueous Phase Liquids or NAPLs) have been particularly difficult. Also treatment of highly soluble but biologically stable organic contaminants such as MTBE and 1,4-dioxane are also quite difficult with many conventional remediation technologies. This is particularly true if these compounds are not significantly naturally degraded, either chemically or biologically, in soil environments. NAPLs present in the subsurface can be toxic to humans and other organisms and can slowly release dissolved aqueous or gas phase volatile organic compounds to the groundwater resulting in long-term (i.e., decades or longer) sources of chemical contamination of the subsurface. In many cases subsurface groundwater contaminant plumes may extend hundreds to thousands of feet from the source of the chemicals resulting in extensive contamination of the subsurface. These chemicals may then be transported into drinking water sources, lakes, rivers, and even basements of homes through volatilization from groundwater.
The U.S. Environmental Protection Agency (USEPA) has established maximum concentration limits for various hazardous compounds. Very low and stringent drinking water limits have been placed on many halogenated organic compounds. For example, the maximum concentration limits for solvents such as trichloroethylene, tetrachloroethylene, and carbon tetrachloride have been established at 5 .mu.g/L, while the maximum concentration limits for chlorobenzenes, polychlorinated biphenyls (PCBs), and ethylene dibromide have been established by the USEPA at 100 .mu.g/L, 0.5 .mu./L, and 0.05 .mu.g/L, respectively. Accordingly, there is a need for improved methods of achieving environmental remediation.
U.S. Pat. No. 7,473,372 broadly discloses the use of chelated species of divalent and trivalent transition metals (particularly iron) to catalyze water soluble peroxygen compounds such as persulfate. By complexing the transition metal catalyst with a chelant, the survivability of the catalyst is greatly enhanced. Although the specific chelants identified in this patent, particularly ethylenediaminetetraacetic acid (EDTA), effectively catalyze persulfate, it would nevertheless be desirable to possess other chelated catalysts which showed enhance activity at the lower temperatures, often of about 10° C. or less, at which the in situ remediation of contaminated environmental media takes place.